Commercial nuclear reactors used for generating electric power include a core composed of a multitude of fuel assemblies which generate heat used for electric power generation purposes. Each fuel assembly includes an array of fuel rods and control rod guide tubes held in spaced relationship with each other by grids of "egg-crate" configuration spaced along the fuel assembly length.
The grids are generally of a first and second plurality of half-slotted Inconel or Zircaloy straps in egg-crate configuration and are spaced along the fuel assembly to provide support for the fuel rods, maintain fuel rod spacing, promote mixing of coolant, provide lateral support and positioning for control assembly guide tubes and provide lateral support and positioning for an instrumentation tube.
The grids along with the control assembly guide tubes and the top and the bottom nozzles form what is known as the skeleton of the fuel assembly. Typically, the guide tubes are screwed into the top and bottom nozzles, the multiple Zircaloy spacer grids are welded to the guide tubes, and the Inconel grid is mechanically attached to the bottom nozzle or guide tube. There is the problem, however, that the skeleton twists from the torquing of the screws as the guide tubes are fastened to the bottom nozzle reducing the straightness of the skeleton. Previously, attaching the Inconel spacer grid to the guide tubes has required complicated machined or welded components which are costly. Thus, it is a problem in the prior art to reliably and economically increase the integrity of the skeleton assembly.